252  MANUFACTURE  OF  CITRIC  ACID  BY  CITRATE  OF  MAGNESIA. 
THE  MANUFACTURE  OF  CITRIC  ACID  BY  CITRATE  OF 
MAGNESIA. 
By  M.  Perret. 
The  manufacture  of  citric  acid  from  lemon  juice  is  an  operation 
of  considerable  delicacy. 
The  industrial  resources  of  Sicily,  and  the  want  of  practical 
processes,  render  this .  fabrication  impossible  on  the  spot  where 
the  fruit  is  produced ;  the  readiness  with  which  lemon  juice,  the 
natural  lemons,  and  the  citiates  of  lime  which  have  been  made 
on  the  spot  become  altered,  occasions  great  losses  to  the  English 
manufacturer,  who  imports  these  various  products  from  Sicily. 
These  considerations,  joined  to  that  of  the  saving  in  cost  of 
transport,  which  would  result  from  producing  the  citric  acid 
in  Sicily  itself,  have  determined  me  to  undertake  some  researches 
in  this  direction,  by  which  I  have  arrived  at  a  very  satisfactory 
process. 
It  consists  in  making  a  tribasic  salt  of  magnesia,  and  trans- 
forming this  salt  into  a  crystallizable  bibasic  salt. 
The  fresh  lemon  juices  are  treated  directly  by  an  excess  of 
magnesia,  which  is  abundant  in  Italy. 
A  perfectly  insoluble  tribasic  citrate  of  magnesia  is  thus 
formed.  This  salt  does  not  become  altered  ;  precipitated  hot  from 
the  juices,  it  is  in  the  form  of  a  granular  powder,  very  dense, 
readily  separating  in  water  (which  softens  it,)  and  which,  seen 
through  a  magnifying  glass,  is  found  to  be  composed  of  a  mass 
of  small  prismatic  crystals  ;  this  powder,  freed  from  mother 
liquor  by  some  cold  washings,  or  by  a  single  washing,  and  dried, 
is  perfectly  unalterable,  resisting  moisture  and  heat  for  a  long 
time  without  becoming  covered  with  mould. 
This  salt,  then,  such  as  it  is,  may  be  despatched  from  the  place 
where  the  citric  acid  is  made ;  but  it  is  evidently  better  to  accu- 
mulate the  acid  upon  this  salt,  and  for  this  purpose  I  treat  a 
given  weight  of  tribasic  citrate  with  a  fresh  quantity  of  lemon 
juice  equal  to  that  which  served  in  the  first  operation  ;  throwing 
the  tribasic  citrate  in  small  portions  into  the  hot  lemon  juice, 
where  it  instantly  dissolves. 
Having  thus  obtained  the  solution  of  bibasic  salt,  I  leave  the 
solution  to  deposit,  decant  and  evaporate  in  vessels  as  wide  as 
